Method for manufacturing a semiconductor-on-insulator structure having low electrical losses, and corresponding structure

ABSTRACT

A manufacturing process for a semiconductor-on-insulator structure having reduced electrical losses and which includes a support substrate made of silicon, an oxide layer and a thin layer of semiconductor material, and a polycrystalline silicon layer interleaved between the support substrate and the oxide layer. The process includes a treatment capable of conferring high resistivity to the support substrate prior to formation of the polycrystalline silicon layer, and then conducting at least one long thermal stabilization on the structure at a temperature not exceeding 950° C. for at least 10 minutes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of the International ApplicationPCT/EP2010/068883, filed Dec. 3, 2010, the entire content of which isexpressly incorporated herein by reference thereto.

BACKGROUND

The present invention relates to a manufacturing process for a structureof a semiconductor on insulator (SeOI) having reduced electrical losses.It also relates to such a structure.

The invention focuses on the general context of manufacturing astructure of semiconductor on insulator type (SOI) by the SmartCut™process. This process is described in detail, for example, in U.S. Pat.No. 5,374,564. A structure of this type generally comprises a supportlayer, typically made of silicon monocrystalline having highresistivity, an insulating oxide layer, and a thin layer ofsemiconductor material. This thin layer is designed to take upcomponents, typically electronic components.

In particular, in applications in which use is made ofradio-frequencies, for example in the field of radiophony, part of theemitted waves can be absorbed by the support substrate, despite thepresence of the insulating layer, resulting in electrical losses. Tocombat this difficulty, it has been proposed to boost resistivity of thesupport substrate to over 500 Ω·cm, or even over a few thousand Ohms·cm,though this does not prove to be sufficient. It was then proposed todeposit on the upper face of the support substrate (that is, the onereceiving the insulating layer and the thin layer), a layer of materialwhereof the density of charge-carrier traps is high. A polycrystallinesilicon layer is adapted in particular to ensure this function. Itsstructure is formed by a multitude of crystalline grains havingdefective boundaries (grain joint) forming traps, which makes theensemble particularly low-conductive. This reduces leakage currents andlosses in resistivity at the level of the support substrate.

The technique to achieve the foregoing structure includes depositing apolycrystalline silicon layer on the support substrate, then applyingthe usual steps of the SmartCut™ process. This type of method isdescribed in particular in US Patent Application 2007/0032042. Whenconducting tests on resulting structures which would exhibit highresistivity according to the teachings of that application, however, itwas found that the technique in question did not reduce electricallosses satisfactorily. Thus, there remains a need for differentsolutions to this problem, and these are now provided by the presentinvention.

SUMMARY OF THE INVENTION

The present invention now provides a manufacturing process for asemiconductor on insulator type structure having reduced electricallosses, in which the polycrystalline silicon layer which is placed onthe support substrate has the expected resistive character.

The process is applied to a substrate successively comprising a supportsubstrate made of silicon, an oxide layer and a thin layer ofsemiconductor material, and having a polycrystalline silicon layerinterleaved between the support substrate and the oxide layer. Theprocess includes oxidizing a donor substrate made of semiconductormaterial to form an oxide layer on a surface thereof; implanting ions inthe donor substrate to form an embrittlement zone therein; bonding thedonor and support substrates together with the oxide layer being locatedtherebetween at a bonding interface, the substrate support having a highresistivity that is greater than 500 Ω·cm, and a polycrystalline siliconlayer on its upper face which is bonded the donor substrate; fracturingthe donor substrate at the embrittlement zone to transfer to the supportsubstrate a thin layer of semiconductor material from the donorsubstrata and form a SeOI structure; and conducting at least one thermalstabilisation of the SeOI structure, at a temperature not exceeding 950°C., and for a time of at least 10 minutes.

The invention also relates to the structures that are provided by themethod. These structures have an average resistivity that is greaterthan 10,000 Ohms·cm.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Other characteristics and advantages of the present invention willemerge from the following description of certain preferred embodiments.This description will be given in reference to the attached diagrams, inwhich:

FIGS. 1A to 1G represent the different steps of the process according tothe invention;

FIG. 2 is a detailed view of part of the structure into which adecoupling layer is interleaved;

FIG. 3 is a variant of FIG. 2 in which an additional decoupling layer isformed on the polycrystalline silicon;

FIG. 4 is a sectional view of a structure according to the inventionwhereof the resistivity is proposed to be tested; and

FIGS. 5A and 5B are graphics respectively illustrating according to theprior art and according to the invention resistivity measured via astructure such as that of FIG. 4, utilising the “SRP” method.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS OF THE INVENTION

The present method is preferably applied to an SOI structure thatsuccessively comprises a support substrate made of silicon, a oxidelayer and a thin layer of semiconductor material, a polycrystallinesilicon layer being interleaved between the support substrate and theoxide layer. The process comprises the following steps:

-   -   a) oxidation of a donor substrate made of semiconductor material        to form an oxide layer at the surface;    -   b) implantation of ions in the donor substrate to form an        embrittlement zone therein;    -   c) adhesion of the donor substrate to the support substrate, the        oxide layer being located at the adhesion interface, the support        substrate having undergone thermal treatment capable of giving        it high resistivity, that is, a resistivity greater than 500        Ω·cm, its upper face which receives the donor substrate being        coated by the polycrystalline silicon layer;    -   d) fracture of the donor substrate according to the        embrittlement zone to transfer to the support substrate a thin        layer of semiconductor material;    -   e) conducting of at least one stabilisation process of the        resulting structure.

This process is remarkable in that the treatment capable of conferringhigh resistivity to the support substrate is carried out prior toformation of the polycrystalline silicon layer, and in that step e)comprises at least one long thermal step, carried out at a temperaturenot exceeding 950° C., for at least 10 minutes.

The polycrystalline silicon is thus deposited after treatment capable ofgiving the support substrate high resistivity, such that hightemperatures utilised during this treatment do not affect thepolycrystalline character of the polycrystalline silicon layer.

Similarly, thermal budget used during thermal treatment of the finalstructure is not sufficient to modify this polycrystalline character.

According to other advantageous and non-limiting characteristics:

-   -   the resistivity of the support substrate is greater than 1,000        Ω·cm, preferably greater than 2,000 Ω·cm, still more preferably        greater than 3,000 Ω·cm;    -   the long thermal step is carried out for several hours;    -   it comprises brief treatment conducted for less than 10 minutes,        at a temperature greater than 1,000° C., advantageously for one        to two minutes, at a temperature of the order of 1,200° C.;    -   thermal treatment capable of conferring high resistivity to the        support substrate comprises at least one step brought to a        temperature of between 500 and 1,200° C., for 30 minutes to 20        hours;    -   thermal treatment capable of conferring high resistivity to the        support substrate is an annealing treatment in three steps, the        second step being brought to a temperature less than that of the        other two steps;    -   the three steps are carried out respectively at a temperature of        between 1,000 and 1,200° C. for 1 to 10 hours, 600 to 900° C.        for 1 to 10 hours, and 900 to 1,200° C. for 1 to 48 hours;    -   in step e), the stabilisation comprises at least one thermal        stabilisation treatment and one thermal thinning treatment of        the thin layer;    -   in step c), prior to depositing of the polycrystalline silicon        layer, a semiconductive decoupling layer of crystalline network,        that is, having a mesh parameter different to that of        monocrystalline silicon is deposited onto the receiver        substrate;    -   the decoupling layer contains polycrystalline silicon;    -   the decoupling layer also contains silicon-based and another        atomic species-based semiconductor material;    -   the silicon-based conductive material is SiC or SiGe;    -   depositing of the decoupling layer and of the polycrystalline        silicon layer is carried out continuously, that is, in the first        instance, by simultaneous feed from two gas sources,        respectively polycrystalline silicon and the other atomic        species, then by feed only from the polycrystalline silicon        source;    -   a new decoupling layer is also deposited onto the        polycrystalline silicon layer;    -   at least one stack constituted by a polycrystalline silicon        layer and a decoupling layer are then deposited onto the new        decoupling layer;

The invention also relates to a structure of semiconductor on insulatortype, with reduced electrical losses, which successively comprises asupport substrate made of silicon, an oxide layer and a thin layer ofsemiconductor material, a polycrystalline silicon layer beinginterleaved between the support substrate and the oxide layer and isremarkable in that the polycrystalline silicon layer has a resistivitygreater than 5,000 Ohms·cm.

Preferably, it has an average resistivity greater than 10,000 Ohms·cm,or even greater than 50,000 Ohms·cm.

As pointed out earlier, the process according to the invention is of theSmartCut™ type.

FIG. 1A accordingly illustrates a donor substrate 1 in silicon (Si),preferably monocrystalline, covered by a layer 10 of silicon dioxide(SiO₂). This corresponds to FIG. 1B.

This oxide layer can result from thermal oxidation of the donorsubstrate 1 or has been formed by conventionally depositing by chemicaldepositing techniques in vapour phase well known to the person skilledin the art under the abbreviations CVD and LPCVD (for “Chemical VaporDeposition” and “Low Pressure Chemical Vapor Deposition”).

With reference to FIG. 1C, the donor substrate is subjected toimplantation of atomic or ionic species via the oxide layer 2.

“Implantation of atomic or ionic species” is understood as anybombardment of these species capable of introducing them to the donorsubstrate with maximal concentration to a predetermined depth of thesubstrate relative to the bombarded surface, with a view to creating anembrittlement zone 13. This type of implantation is done according tothe process known by the name SmartCut™

The embrittlement zone 13 delimits a thin layer 11 from the rest 12 ofthe donor substrate 1.

The implantation of atomic or ionic species can be simple implantation,that is, implantation of a single atomic species such as for exampleimplantation of hydrogen, helium or noble gas.

Implantation can also be co-implantation of atomic or ionic species,such as helium and hydrogen.

A receiver substrate 2 is illustrated in FIG. 1D, and is a solidsubstrate made of silicon.

A characteristic of this support substrate is having undergone thermaltreatment capable of giving it an other resistivity, that is, aresistivity greater than 500 Ω·cm, or even greater than 1,000,preferably still greater than 2,000, or even still more preferablygreater than 3,000 Ω·cm.

This treatment can have been carried out since fabrication of thesubstrate or later on, within the scope of the present process.

This thermal treatment capable of giving the support substrate 2 highresistivity is a thermal treatment for example, comprising at least onestep brought to a temperature of between 500 and 1,200° C. for 30minutes to 20 hours.

In another embodiment, this treatment comprises annealing treatment inthree steps, the second step being brought to a temperature less thanthat of the other two steps.

Advantageously, these three steps are carried out respectively at atemperature of between 1,000 and 1,200° C. for 1 to 10 hours, 600 to900° C. for 1 to 10 hours and 900 to 1,200° C. for 1 to 48 hours.

The function of the first step of this advantageous and optionaltreatment, also known as “High-low-High treatment”, is to remove oxygenfrom a superficial zone of the substrate, by a phenomenon known as“exodiffusion” to produce denuded zone, that is, a zone without oxygenprecipitates. This is therefore a zone having fewer defects than at theoutset, an advantage for subsequent depositing of polysilicon.

The aim of the second step of this process is to enable nucleation, thatis, the creation of “embryos” of interstitial oxygen precipitates.

Finally, the function of the third step of this process is to enablegrowth of precipitates created in the preceding step, that is,constitute oxide clusters. This translates via an increase inresistivity of the material.

In any case, this augmentation treatment of the resistivity of thesubstrate 2 is carried out prior to depositing, on the latter, of apolycrystalline silicon layer 20.

Proceeding with this effectively retains the polycrystalline structureof the layer 20.

After the donor substrate 1 is reversed, it is then put in contact withthe layer 20 of the support substrate 8, such that the oxide layer 10regains contact with the polysilicon layer 20.

Adhesion between the two substrates is completed in a preferred butnon-obligatory manner, by molecular adhesion.

Disbonding annealing is carried out, followed by detachment from therest 12 of the donor substrate 1, at the level of the embrittlement zone13, so as to transfer the layer 11 to the support substrate 2, moreprecisely on the polysilicon layer 20.

This produces a substrate 3 of semiconductor on insulator type which isin semi-finished state.

Stabilisation of the resulting structure 3 is then carried out.

In keeping with the invention, this stabilisation comprises a longthermal step, carried out at a temperature not exceeding 950° C. for atleast 10 minutes, and optionally a brief treatment carried out for lessthan 10 minutes at a temperature greater than 1,000° C.

The long thermal step is preferably carried out for several hours,whereas the brief treatment is carried out for 1 to 2 minutes at atemperature of the order of 1,200° C.

More precisely, these finishing steps comprise at least one of thefollowing treatments:

a) thermal stabilisation treatment before polishing, consuming the zoneof the donor substrate damaged by separation at the level of theinterface 13;

b) mechanical and chemical polishing treatment (CMP) for consuming thematerial of the layer 11 to arrive at the preferred thickness;

c) final thermal thinning treatment to attain the final preferredthickness.

In respecting the temperature and duration conditions indicated earlier,thermal budgets carried out are inadequate for recrystallisedpolysilicon which loses its beneficial effects.

But, limiting the duration and/or temperature of the treatments duringstabilisation of the structure causes embrittlement of the interfacecreated such that it is highly useful to carry out intermediatetreatments for reinforcing cohesion of the structure. A particulartreatment is carried out prior to adhesion using plasma.

In accordance with a preferred embodiment of the process according tothe invention, the polycrystalline silicon layer is formed on a layer 21known as “network crystalline decoupling”, that is, a layer having aconcentration gradient with a mesh parameter different to that ofsilicon formed by the support substrate.

This difference in mesh parameter is for example greater than 5%.

This decoupling layer advantageously contains polycrystalline silicon,but in no case pure monocrystalline silicon.

According to a preferred embodiment, it also contains a silicon-basedand another atomic species-based semiconductor material.

This can be SiC or SiGe for example.

The advantage of this gradient layer between the support substrate 2 andthe polysilicon layer is that it prevents the polysilicon fromrecrystallising from the layer 11.

This gradient layer opposes recrystallisation of polysilicon. Via itscavities and grain joints, the polysilicon layer:

-   -   traps the contaminants generating a drop in resistivity (B, P,        Ca, Na, etc.);    -   forms a barrier to electrical charges contained under the oxide        10;    -   prevents diffusion of interstitial oxygen contained in the oxide        10 (diffusion causing poor trapping, such as a “gettering”        effect).

The decoupling layer 21 as well as the polysilicon layer 20 arepreferably manufactured in the same depositing step, continuously,meaning that the layer 21 is first formed by injecting a first gas toconstitute polysilicon and a second gas to constitute the other atomicspecies; then, once the preferred thickness is attained the arrival ofthe second gas is cut off by continued injecting of the gas to form thepolysilicon layer.

As shown in FIG. 3, a new decoupling polysilicon layer can also beconstituted, which prevents the latter from recrystallising from thethin layer of semiconductor material 11.

Optionally, a stack comprising decoupling layer 21/polysilicon layer20/decoupling layer 21/polysilicon layer 20, etc. can be formed.

Advantageously, the total thickness of the polysilicon layer and of thedecoupling layer or decoupling layers is between 3,000 and 10,000 Å,with a ratio 10 between the thickness of the polysilicon layer and thedecoupling layer.

FIG. 4 proposes testing the resistivity of a structure obtainedaccording to the invention.

This characterisation is done by means of the well-known method called“4PP” (for “four points probe”), specifically by using 4 electrodespassing through the entire structure.

A second method known as “SRP”, also well known, traces the evolution ofresistivity as a function of the depth, by means of a mitre, as shown bythe above-mentioned figure.

Irrespective of the method used, it is evident that the structuretreated according to the process according to the invention retains highresistivity, compared to the same structure which would not haveundergone the process according to the invention.

Using the method known as 4PP and by conducting comparative tests,average resistivity rises from 4 to 5,000 Ω·cm to over 70,000 Ω·cm.

Furthermore and as shown in FIGS. 5A and 5B, the method known as “SRP”tested on a structure according to the prior art cited at the outset ofthe description (FIG. 5A), comparatively to the invention (FIG. 5B),shows that according to the invention the polysilicon layer has veryhigh resistivity, contrary to the structure according to the prior art.

This is due to the fact that the polysilicon has retained itspolycrystalline structure.

Finally, tests were conducted by “injecting” an electrical signal in acomponent.

The power of harmonics as a function of the principal signal is thenmeasured.

When components used in the field of radio-frequencies are operating,parasite signals can be generated by the electrical signals which passthrough them at different frequencies. These are known as harmonicwaves.

In the case of a glass substrate, almost no harmonic is generated, andthe more the substrate on which the component electronic is made ishigh-performing, the less is the power of the harmonics.

In the case of a support substrate 2 made of high-resistivity silicon,without the presence of a polycrystalline silicon layer under the Box,the harmonics are high.

With the presence of such a layer, though without modifying thermaltreatments, electrical performance is improved, but thermal budgetcauses partial recrystallisation or even total recrystallisation of thepoly-Si and eliminates significant electrical traps.

Finally, the presence of polycrystalline silicon under the Boxconsiderably improves electrical performance, since the manufacturingprocess is applied according to the invention and/or a decoupling layer(21) is introduced which prevents recrystallisation of the silicon.

It is evident, finally, that depositing a gradient layer between thesupport substrate and the polycrystalline silicon can also be carriedout within the scope of manufacturing a structure of SOI type, otherthan by the SmartCut™ technique.

1. A manufacturing process for preparing a semiconductor on insulatorstructure that exhibits type reduced electrical losses, the substratesuccessively comprising a support substrate made of silicon, an oxidelayer and a thin layer of semiconductor material, and having apolycrystalline silicon layer interleaved between the support substrateand the oxide layer, which process comprises: oxidizing a donorsubstrate made of semiconductor material to form an oxide layer on asurface thereof; implanting ions in the donor substrate to form anembrittlement zone therein; bonding the donor and support substratestogether with the oxide layer being located therebetween at a bondinginterface, the substrate support having a high resistivity that isgreater than 500 Ω·cm, and a polycrystalline silicon layer on its upperface which is bonded the donor substrate; fracturing the donor substrateat the embrittlement zone to transfer to the support substrate a thinlayer of semiconductor material from the donor substrate and form a SeOIstructure; and conducting at least one thermal stabilisation of the SeOIstructure, at a temperature not exceeding 950° C., and for a time of atleast 10 minutes.
 2. The process of claim 1, wherein the resistivity ofthe support substrate is greater than 1,000 Ω·cm and is obtained by athermal treatment carried out prior to the providing the polycrystallinelayer thereon.
 3. The process of claim 1, wherein thermal stabilizationis carried out for several hours.
 4. The process of claim 1, whichfurther comprises a rapid thermal treatment carried out over a period ofless than 10 minutes and at a temperature greater than 1,000° C.
 5. Theprocess of claim 1, wherein thermal treatment comprises heating to atemperature of between 500 and 1,200° C. for 30 minutes to 20 hours. 6.The process of claim 2, wherein thermal treatment is an annealingtreatment conducted over three steps, with the second step requiringheating to a temperature that is less than that of the first and thirdsteps.
 7. The process of claim 6, wherein the three steps are conductedrespectively at a temperature of between 1,000 and 1,200° C. for 1 to 10hours, 600 to 900° C. for 1 to 10 hours, and 900 to 1,200° C. for 1 to48 hours.
 8. The process of claim 1, wherein thermal stabilisationcomprises at least one thermal stabilisation treatment and one thermalthinning treatment of the thin layer.
 9. The process of claim 1, whichfurther comprises prior to depositing of the polycrystalline siliconlayer depositing on the receiver substrate a semiconductive decouplinglayer having a mesh parameter different to that of siliconmonocrystalline.
 10. The process of claim 9, wherein the decouplinglayer contains polycrystalline silicon.
 11. The process of claim 10,wherein the decoupling layer also contains another atomic species-basedsemiconductor material.
 12. The process claim 11, wherein thesilicon-based material conductor is SiC or SiGe.
 13. The process ofclaim 11, wherein the depositing of the decoupling layer and thepolycrystalline silicon layer are carried out continuously, by asimultaneous feed from two gas sources, one of which is polycrystallinesilicon and the other of which is the other atomic species, then by feedonly from the source of polycrystalline silicon.
 14. The process ofclaim 9, which further comprises depositing a further decoupling layeron the polycrystalline silicon layer.
 15. The process of claim 14, whichfurther compromises depositing at least one stack constituted by apolycrystalline silicon layer and a decoupling layer on the furtherdecoupling layer.
 16. A semiconductor-on-insulator structure havingreduced electrical losses, which successively comprises a supportsubstrate made of silicon, an oxide layer and a thin layer ofsemiconductor material, and a polycrystalline silicon layer interleavedbetween the support substrate and the oxide layer, wherein thepolycrystalline silicon layer has a resistivity that is greater than5,000 Ohms·cm.
 17. The structure of claim 16, having an averageresistivity that is greater than 10,000 Ohms·cm.